1. Field of the Invention
The present invention relates to an optical module having a light emitting element, a mounting method of the same, and an optical module mounted substrate, and more particularly, to an optical module in which a surface light emitting element is used as a light emitting element, a mounting method of the same, and an optical module mounted substrate.
2. Description of the Related Art
When an optical module having a light emitting element is mounted on a waveguide substrate, the optical module must be very precisely positioned relative to the waveguide substrate. For example, when an optical multi-chip module (optical MCM) having a light emitting element is mounted on a substrate in which a waveguide is formed, positioning between a waveguide core and a light emitting point of the light emitting element must be positioned very precisely, for example, within ±5 μm or less. As the light emitting element, a surface light emitting element such as a VCSEL is generally used. For positioning (alignment), there are an active alignment method and a passive alignment method. Next, these methods will be described.
FIGS. 1A and 1B are views showing an example of positioning by the active alignment, in which FIG. 1A is a top view of a waveguide substrate, and FIG. 1B is a side view showing a method of mounting an optical module (optical MCM) on the waveguide substrate. As shown in FIG. 1A, a waveguide 2 and plural electrical connection pads 3 around it are provided on a waveguide substrate 1. The waveguide 2 includes a waveguide core 4 of, for example, about 50 μm×50 μm and a waveguide cladding 5 surrounding it. As shown in FIG. 1B, the waveguide 2 extends in the vertical direction from the upper surface of the waveguide substrate 1 to the inside, forms a reflecting surface at a halfway point, turns to the horizontal direction, and leads to the side surface of the waveguide substrate 1. A light receiving element 6 is provided at the side surface of the waveguide substrate 1. An optical MCM 7 includes a light emitting element 8 (for example, a surface light emitting element such as a VCSEL), an element drive circuit 9, and a bump 10 for electrical connection, and is held by a hand 11 for position adjustment. The active alignment is performed as described below. First, when the optical MCM 7 is mounted on the waveguide substrate 1, electric power is supplied to the optical MCM 7 during the mounting process, and the light emitting element 8 emits light. While the position of the optical MCM 7 is adjusted by the hand 11, the light from the light emitting element 8 is monitored by the light receiving element 6 provided at the side surface of the waveguide substrate 1 to find a position where coupling efficiency is high. When the coupling efficiency is high, the position of the optical MCM 7 is fixed by the bump 10. By this, the positioning using the active alignment is complete.
FIGS. 2A to 2C are views showing an example of positioning by the passive alignment, in which FIG. 2A is a top view of a waveguide substrate, FIG. 2B is a side view showing a method of mounting an optical module (optical MCM) on the waveguide substrate, and FIG. 2C is a view for explaining a method of positioning. In FIGS. 2A to 2C, the same reference numerals as those of FIG. 1 denote similar parts.
In the passive alignment, as shown in FIG. 2B, an upper/lower recognition camera 21 is used. The passive alignment is performed as described below. First, a light emitting point of a light emitting element 8 and a waveguide core are recognized by an image recognition device of a mount device through the upper/lower recognition camera 21, and as shown in FIG. 2C, an optical MCM 7 is moved by a position adjustment hand 11 so that a center position 12 of the light emitting point of the light emitting element 8 becomes coincident with a center position 13 of the waveguide core. That is, the positions are precisely adjusted within ±5 μm. When the positioning is precisely performed, the optical MCM 7 is fixed by a bump 10. By this, the positioning using the passive alignment is complete.
However, the related art is subject to a number of limitations. First, because the mount precision of a chip mounter used in typical surface mount technology (SMT) is approximately ±20 μm, sufficiently high precision mounting is not achieved. Alternatively, to perform the surface mount at high precision, expensive equipment is needed. In addition, since high precision positioning takes a long time, and therefore, mass production cannot be achieved with high precision according to the related art.